Extended Abstract (68K)11A.3
A relationship between a surface theta-e ridge and dominant lightning polarity
Nettie R. Lake, Lyndon State College, Lyndonville, VT; and D. R. MacGorman
For many years, it was believed that cloud-to-ground lightning lowered only negative charge to the ground (-CG flashes). In the past twenty years, however, flashes lowering positive charge (+CG flashes) have been documented and studied. This presentation summarizes positive correlations between +CG flashes, hail, and tornadoes. Recent studies have reported that in some cases, dominant storm polarity reverses from positive to negative. Additionally, it has been observed that 50% of such storms are tornadic, and that tornadoes usually occur during or after the reversal. Smith et al. (2000) observed that polarity reversals often occur at surface equivalent potential temperature (theta-e) ridges. This study examined dominant polarity patterns of severe storms during the entire year 1999. Similar to Smith et al. (2000), this study found that 82% of polarity reversals occur at a theta-e ridge. Furthermore, positively dominated storms that move parallel to a ridge axis seldom reverse polarity. Also, negative storms do not reverse polarity relative to a theta-e ridge. Explanations for why polarity reversals may occur at a theta-e ridge will also be discussed.
Session 11A, Lightning Studies
Wednesday, 14 August 2002, 4:30 PM-6:00 PM
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